JP4843790B2 - Temperature measurement method using ultrasonic waves - Google Patents

Description

  The present invention relates to a temperature measurement method using ultrasonic waves that measures the temperature distribution of a medium using ultrasonic waves.

  Conventionally, the surface temperature of an object to be measured can be measured by a contact-type thermometer using a thermocouple or a radiation thermometer using radiation.

  In addition, temperature measurement using ultrasonic waves is known that uses temperature dependence in which the propagation speed of ultrasonic waves incident on the medium depends on the temperature of the medium, and a method for measuring the temperature of a medium such as a gas or a solid material (for example, a patent) Documents 1 to 3) have been proposed.

By the way, there are many material processing processes in the high temperature environment, and there are many requests for non-destructive and in-process measurement of the temperature of various materials and the temperature distribution therein. Then, even if the internal temperature could be measured, the temperature distribution could not be measured.
JP-A-53-124486 Japanese Patent Laid-Open No. 57-16874 JP 2000-234963 A

  Therefore, an object of the present invention is to provide a temperature measurement method using ultrasonic waves that can measure the temperature distribution in the medium by propagating the ultrasonic waves in the medium.

According to the first aspect of the present invention, an ultrasonic probe is disposed on one side of the medium, the other side of the medium is heated, and the propagation time of the ultrasonic pulse propagating a certain distance in the medium is known. a from the data the temperature measuring method of the temperature distribution using ultrasound you measure in the medium,
Using the propagation speed of the ultrasonic pulse with respect to the temperature of the medium and the temperature conductivity of the medium as the known data, the ultrasonic pulse is incident from one side of the medium by the ultrasonic probe. And measuring the propagation time of the ultrasonic pulse reflected from the other side of the medium,
Assuming a function T (x, t) indicating the temperature distribution of the medium determined by the initial temperature of the medium, the temperature conductivity of the medium, and the measurement time after the heating, and before the heating, From the initial temperature obtained by measuring the surface temperature, the known temperature conductivity of the medium, the measurement time after the heating, and the propagation time of the measured ultrasonic pulse, the known temperature This is a method of calculating the other side surface temperature and temperature distribution of the medium by using the equation of the propagation time of the ultrasonic pulse obtained from the propagation speed of the ultrasonic pulse with respect to the temperature of the medium and the function T (x, t). .

In the invention of claim 2, the propagation time formula is

And in Equation 1, t _L Is the propagation time of the ultrasonic pulse, V (T) is the sound speed of the medium expressed as a function of the temperature T, and this sound speed V (T) is expressed by the following formula 2.

  In the above equation 2, A and B are constants specific to the medium,
  The function T (x, t) is

In Equation 3, η is expressed by Equation 4 below,

数３及び数４において、Ｔsは他側面温度、Ｔ ₀ は媒体の初期温度、αは温度伝導率（α＝λ/ρＣ：λは媒体の熱伝導率、ρは媒体の密度、Ｃは媒体の比熱容量）、ｘは他側面からの距離、ｔは加熱後の測定時間、ｕは確率変数である方法である。

In Equations 3 and 4, Ts is the other side surface temperature, T ₀ is the initial temperature of the medium, α is the temperature conductivity (α = λ / ρC: λ is the thermal conductivity of the medium, ρ is the density of the medium, and C is the medium density. Specific heat capacity), x is the distance from the other side, t is the measurement time after heating, and u is a random variable .

The invention of claim 3 is a method in which the surface of the medium is one side surface, and the temperature of one side surface of the medium is measured to obtain the initial temperature .

According to a fourth aspect of the present invention, the ultrasonic pulse is incident obliquely from one side.

The invention of claim 5 is a method in which a frequency of the ultrasonic pulse is 100 kHz or more.

According to the above configuration, since the temperature distribution in the medium is measured from the propagation time of the ultrasonic wave propagating in a certain distance in the medium and the known data of the medium, the velocity of the ultrasonic wave in the medium is The temperature distribution of the medium determined by the initial temperature of the medium, the temperature conductivity of the medium, and the measurement time after heating is shown without using a thermocouple or the like inside the object to be measured. function T (x, t) and, using the formula for propagation time of the ultrasonic pulse obtained by the propagation speed of the ultrasonic pulse with respect to the temperature of the known medium, the medium from the known data regarding propagation speed and medium ultrasonic pulse It is possible to measure the temperature distribution. In addition, the time response is superior to the conventional temperature measurement method.

In addition, as the known data of the medium, ultrasonic velocity data with respect to the temperature of the medium and the temperature conductivity of the medium can be used.

  Furthermore, the ultrasonic pulse echo method and the pitch catch method (oblique incidence method) can be used by using the ultrasonic pulse, the measurement can be performed on one side of the medium, and an object having a different temperature on the other side of the medium. Can be measured in a state in which is placed.

  Furthermore, the surface temperature of the medium and the temperature of one side surface can also be measured, and the ultrasonic pulse is preferably 100 kHz to several MHz (less than 10 MHz).

  Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below do not limit the contents of the present invention described in the claims. In addition, all of the configurations described below are not necessarily essential requirements of the present invention. In each example, by employing a temperature measurement method using ultrasonic waves that is different from the conventional one, a temperature measurement method using ultrasonic waves that has never been obtained can be obtained, and the temperature measurement method using the ultrasonic waves is described respectively. To do.

  Embodiment 1 of the present invention will be described below with reference to FIGS.

  In a wide range of engineering and industrial fields, there are many needs to accurately measure the temperature inside an object in real time. In this example, SKD steel used as a die casting mold was used as a medium.

  FIG. 1 shows a temperature measuring apparatus 1, and as shown in FIG. 1, an SKD plate 2 having a thickness of 30 mm is used as a medium. The plate 2 is formed in a block shape and includes a parallel upper surface 3 and a bottom surface 4. And is arranged so that the bottom surface 4 is in contact with the hot water 6 put in the container 5.

  An ultrasonic probe 12 is disposed on the upper surface 3 via a coupler 11, and the ultrasonic probe 12 includes a transducer (not shown) that generates ultrasonic waves, and an ultrasonic wave from the transducer. Is incident on the plate material 2 and detects the ultrasonic wave returned from the plate material 2, and has functions of a wave transmitting means and a wave receiving means, and in this example, an ultrasonic pulse echo reflected from the bottom surface 4. Is detected.

  The ultrasonic probe 12 is connected to a detection control means 13, and the detection control means 13 controls the ultrasonic pulse incident on the plate 2 and the waveform of the returned ultrasonic pulse echo and the time until the return. The propagation time and the like are detected, and the detected data is output to the arithmetic processing control means 15 by the waveform data output means 14. The arithmetic processing control means 15 is a computer equipped with storage means. The arithmetic processing control means 15 is based on the detection data input from the waveform data output means 14 and the known data of the plate 2 and the like. Based on the theoretical formula, the temperature distribution including the inside of the plate member 2 is calculated and displayed on the display means 16 such as a display, and the waveform of each state of the ultrasonic pulse is controlled to be displayed.

  For the experiment, a contact-type temperature measuring means was provided along with the apparatus 1. Seven thermocouples 21, 21,... Were used as the temperature measuring means. The thickness W of the plate 2 used in the experiment is 30 mm, and thermocouples are provided at six locations of the bottom surface position W1, the top surface position W6, and the positions W2, W3, W4, and W5 spaced from the bottom surface 4 by 5 mm. 21 was further disposed, and a thermocouple 21 was also disposed at a position W7 where the temperature of the hot water 6 was measured. The temperature detection means 22 calculates the temperature from the detection data detected by these thermocouples 21, and the temperature data is sent to the arithmetic processing control means 15, which calculates the temperature measured by the thermocouple 21. It can be displayed on the display means 16. In this example, twice the thickness W is the propagation distance of the ultrasonic wave in the medium.

  Next, the principle relating to the temperature measurement of the present invention will be described. Assuming an object (medium) having a one-dimensional temperature distribution, the propagation time of the ultrasonic wave propagating through the object can be expressed by Equation 1 below.

上記数１で、Ｖ（Ｔ）は温度Ｔの関数として表される物体の音速であり、近似的に下記の数２で表すことができる。

In the above equation 1, V (T) is the sound velocity of the object expressed as a function of the temperature T, and can be approximately expressed by the following equation 2.

上記数２で、Ａ，Ｂは、それぞれ物体固有の定数である。今、一様な温度Ｔ₀を持つ半無限物体物の片面が高温物体と接触することにより熱せされる状態を考えると、一次非定常状態において物体内部での発熱や対流がなく温度伝導率が温度に依存しないとき、接触後（加熱後）の接触面温度は、一定値Ｔ_Sに保持される。このときの物体内の温度分布Ｔ(x,t)は、下記の数３及び数４で表すことができる。

In the above equation 2, A and B are constants specific to the object. Considering a state where one surface of a semi-infinite object having a uniform temperature T ₀ is heated by contact with a high-temperature object, there is no heat generation or convection inside the object in the primary unsteady state, and the temperature conductivity is When not dependent on temperature, the contact surface temperature after contact ( after heating) is maintained at a constant value T _S. The temperature distribution T (x, t) in the object at this time can be expressed by the following equations 3 and 4.

上記数３及び数４で、Ｔsは接触面温度、Ｔ₀はその初期温度、αは温度伝導率（α＝λ/ρＣ：λは熱伝導率、ρは密度、Ｃは比熱容量）、ｘは接触面からの距離、ｔは接触後（加熱後）の測定時間である。数３の右辺第二項は確率変数ｕで表される誤差関数に（Ｔ₀−Ｔs）を乗じた形となっている。超音波伝播時間ｔ_Lを計測することで、数１〜数４を用いて、温度Ｔsを求めることができる。但し、初期温度Ｔ₀、温度伝導率α、時間ｔは既知とする。

In the above formulas 3 and 4, Ts is the contact surface temperature, T ₀ is the initial temperature, α is the temperature conductivity (α = λ / ρC: λ is the thermal conductivity, ρ is the density, and C is the specific heat capacity), x Is the distance from the contact surface, and t is the measurement time after contact (after heating) . The second term on the right side of Equation 3 has a form obtained by multiplying the error function represented by the random variable u by (T ₀ −Ts). By measuring the ultrasonic propagation time t _L , the temperature T s can be obtained using Equations 1 to 4. However, the initial temperature T ₀ , the temperature conductivity α, and the time t are assumed to be known.

  Experiments were performed using the apparatus shown in FIG. 1, and the thickness of the plate 2 was 30 mm as described above, and an ultrasonic probe 12 having a frequency of 5 MHz was installed on the upper surface 3 of the plate 2 to measure ultrasonic pulse echo. Went. A cross-correlation method was used to measure the ultrasonic wave propagation time t in the plate 2. The arithmetic processing control means 15 simultaneously measures the ultrasonic pulse echo and temperature by a monitoring system using general-purpose software, and records the ultrasonic waveform and temperature at a rate of 5 times / second, respectively. The state where the bottom surface 4 of 21 was in contact with the warm water 6 at 75 ° C. was monitored.

  FIG. 2 is a graph in which the vertical axis represents the amplitude of the ultrasonic pulse echo, the other vertical axis represents the temperature, and the horizontal axis represents the measurement time. The temperature is a position W1 of 5 mm from the bottom surface 4 to the top surface side of the plate 2. The measurement result of the position W5 of 25 mm and the temperature change on the bottom surface 4 side and the top surface 3 side of the plate member 2 is shown. It is observed that the intensity (amplitude) of the ultrasonic pulse echo is sharply reduced, which is based on the contact between the bottom surface 4 of the plate member 2 and the hot water 6. In other words, this is due to a decrease in the reflectance of the ultrasonic wave due to the contact between the bottom surface 4 and the hot water 6, and the decrease in the intensity of the ultrasonic pulse echo substantially coincides with the theoretically calculated change in reflectance (6%). Thus, contact with the hot water 6 can be detected with high accuracy by using the ultrasonic pulse echo as an index.

  The temperature change by the thermocouple 21 installed at the position W1 5 mm from the bottom surface 4 was confirmed about 0.5 seconds after the time when the intensity of the ultrasonic pulse echo started to decrease.

  FIG. 3 is a graph showing temperature changes with the vertical axis representing temperature and the horizontal axis representing measurement time, and for comparison with the results of temperature measurement according to the present invention using “ultrasonic waves” (hereinafter referred to as ultrasonic method). Shows the results of temperature measurement using a "thermocouple". Both trends are in good agreement. At the position W1 5 mm from the bottom surface 4, there is a difference between them, but the ultrasonic method catches the temperature rise about 0.5 seconds earlier than the temperature measurement using the thermocouple 21.

  FIG. 4 is a graph in which temperature is plotted on the vertical axis and distance from the bottom surface 5 is plotted on the horizontal axis, and “thermocouple” is used for comparison with the results of temperature measurement according to the present invention using “ultrasonic waves”. The results of temperature measurement are shown. The temperature distribution at 1 second after the bottom surface 4 was in contact with the hot water 6 substantially coincided with that of the thermocouple 21, but there was a difference between the two near the bottom surface 4 over time. The cause is considered to be effects such as convection of the hot water 6 and heating from the side surface of the plate member 2, and it is considered that practical measurement of temperature becomes possible by suppressing these influences or correcting the calculation.

  Thus, in the present embodiment, corresponding to claim 1, the temperature distribution T (in the plate material 2 is obtained from the propagation time t of the ultrasonic wave propagating a certain distance in the plate material 2 as a medium and the known data of the plate material 2. x, t) is measured, and the propagation speed of the ultrasonic wave is utilized without inserting a thermocouple 21 or the like into the measurement object 2 using the fact that the velocity of the ultrasonic wave 2 in the plate 2 depends on the temperature. It is possible to measure the temperature distribution T (x, t) in the plate 2 from known data relating to the above. In addition, the time response is superior to the conventional temperature measurement method.

Further, in the present embodiment in this manner, corresponding to claim 1, the known data, using an ultrasound velocity data with respect to the temperature of the plate 2, also corresponding to claim 1, known data In addition, since the data of the temperature conductivity α of the plate material 2 is used, calculation by estimating the temperature distribution T (x, t) is possible.

In this way, in this embodiment, in response to claim 1 , since the ultrasonic wave is an ultrasonic pulse, an ultrasonic pulse echo method or a pitch catch method (oblique incidence method) can be used, Measurement can be performed on the upper surface 3 that is one side of the plate member 2, and measurement can be performed in a state where hot water 6 that is an object having a different temperature is disposed on the bottom surface 4 that is the other side of the plate member 2.

In this way, in this embodiment, corresponding to claim 1 , the ultrasonic pulse is incident from the upper surface 3 that is one side surface of the plate material 2 that is a medium, and is reflected by the bottom surface 4 that is the other side surface of the plate material 2. Since the propagation speed of the echo is measured, the measurement can be performed on the upper surface 3 which is one side of the plate material 2, and the measurement can be performed in a state where the hot water 6 which is an object having a different temperature is arranged on the bottom surface 4 which is the other side of the plate material 2. .

In this way, in this embodiment, corresponding to claim 1 , an ultrasonic pulse is incident from the upper surface 3 that is one side surface of the plate material 2 that is a medium, and the plate material 2 and the temperature are incident on the bottom surface 4 that is the other side surface of the plate material 2. Since the hot water 6 which is a different object is disposed, measurement on one side of the plate member 2 is possible.

Further, in the present embodiment in this manner, corresponding to claim 1, from measuring the surface temperature of the medium serving plate 2, together with the internal temperature distribution can be measured by calculating by estimating the surface temperature.

In this way, according to the third embodiment, since the upper surface 3 as one side surface of the plate material 2 as a medium is measured, the measurement is performed by estimating and calculating the surface temperature together with the internal temperature distribution. it can.

In this way, in this embodiment, the frequency of the ultrasonic pulse is 100 kHz or more, corresponding to claim 5 .

Corresponding to claim 2, the above _equations 1 to 4 are used, where Ts is the contact surface temperature, T ₀ is the initial temperature, α is the temperature conductivity (α = λ / ρC: λ is the heat Conductivity, ρ is density, C is specific heat capacity), x is a distance from the contact surface, t is a measurement time after contact (after heating) , u is a random variable, and ultrasonic propagation time tL is measured. The temperature Ts can be obtained, and the temperature distribution T (x, t) of the medium can be obtained.

Reference example 1
5 to 8 show a reference example 1 of the present invention, the same reference numerals are given to the same parts as those of the above-described embodiment 1, detailed description thereof is omitted, and the temperature measuring device 1 of this reference example is In addition to using the mold 5A in place of the container 5, molten aluminum 6A is put in the mold 6A in place of the hot water 6. Further, the thermocouple 21 is placed at the surface position W6 of the plate member 2, the position W1 ′ 4 mm above the bottom surface 4 of the plate member 2, and the positions W2 ′, W3 ′, W4 ′, W5 ′ at intervals of 5.5 mm from this position W1 ′. The upper surface position W6 and the position W5 ′ are 4 mm apart. Moreover, the thermocouple 21 (position W7) which measures the temperature of the molten aluminum 6A is provided.

In Example 1, the temperature distribution T (x, t) is expressed by Equation 3 and Equation 4. In this reference example, the temperature distribution T (x, t) in the object depends on the boundary condition, but here, an exponential function as shown in Equation 5 below is approximately assumed.

上記数５で、ｘは距離、Ｃ，Ｄ，Ｅは定数である。超音波パルスエコーの計測二より物体内の超音波伝播時間ｔLを精度良く測定すれば、上記の式から物体内の任意の位置での温度を求めることができ、また、近似的に内部の温度勾配を推測することもできる。尚、この例では、物体内の一点の温度を既知情報として用いることとする。

In the above equation 5, x is a distance, and C, D, and E are constants. If the ultrasonic propagation time tL in the object is accurately measured from the measurement of the ultrasonic pulse echo, the temperature at an arbitrary position in the object can be obtained from the above formula, and the internal temperature can be approximated. The slope can also be inferred. In this example, the temperature at one point in the object is used as known information.

  FIG. 6 shows the results of measuring the temperature dependence of the sound speed of the plate 2. This experiment was performed in a state where the temperature in the thickness direction of the plate material 2 was made uniform using a heater for heating separately prepared. From this result, it can be seen that within this temperature range, the speed of sound can be expressed by a linear equation of temperature, as assumed in Equation 2 above. For later temperature estimation, the relational expression obtained by the least square method is used.

  FIG. 7 is a graph in which the vertical axis represents the amplitude of the ultrasonic pulse echo, the other vertical axis represents the temperature, and the horizontal axis represents the measurement time. The plate material before and after the molten aluminum 6A contacts the bottom surface 4 of the plate material 2. 2 shows the intensity of the ultrasonic pulse echo from the bottom surface 4 of 2 and the temperature change at the positions W1 ′ and W5 ′ of the plate 2. When attention is paid to the ultrasonic pulse echo, the decrease in intensity is clearly confirmed at the point a. This is because molten aluminum 6A is in contact with the bottom surface 4 of the plate 2 and a part of ultrasonic energy is transmitted from the bottom surface 4 to the molten aluminum 6A. Can accurately capture the contact situation. Hereinafter, this point a is set as a reference time for starting contact. Note that the temperature rise at the thermocouple 21 (position W1 ′) located closest to the bottom surface 4 is about 1.7 seconds after point a. It can be seen that the time response is superior to that of the pair 21. Naturally, the temperature change of the thermocouple 21 at the position W5 ′ far from the bottom surface 4 was slower than the thermocouple 21 at the position W1 ′. In this example, the ultrasonic propagation time tL and the temperature near the upper surface 3 are used as measurement known information for the estimation of the internal temperature. Here, the temperature of W5 ′ close to the upper surface 3 is used as the known information. Thus, in addition to the known physical data of the medium, one piece of information (data) related to the temperature at the time of measurement may be added and used.

FIG. 8 is a graph showing the temperature change with the vertical axis representing temperature and the horizontal axis representing measurement time. The result of temperature measurement according to the present invention using “ultrasonic waves” was used for comparison with “thermocouple”. The results of temperature measurement are shown. Both tendencies were in good agreement, confirming the effectiveness of the measurement method of this reference example .

Reference example 2
FIG. 9 shows a reference example 2 of the present invention, in which the same reference numerals are given to the same parts as those in the first embodiment, and detailed description thereof is omitted. In this reference example, one side of the plate material 2 as a medium is shown. A transmitting ultrasonic probe 12A is provided on the other side, and a receiving ultrasonic probe 12B is provided on the other side of the plate 2. The ultrasonic probe 12B receives an ultrasonic pulse incident on the plate 2 from the ultrasonic probe 12A, and a certain distance of the medium has a thickness W.

In the first embodiment and the reference example 1 , the so-called pulse echo method has been described. However, a pitch catch method (oblique incidence method) may be used, that is, although not shown, the ultrasonic probes 12A and 12B are used. Provided on one side of the medium, an ultrasonic pulse from the ultrasonic probe 12A is obliquely incident on the one side, and an ultrasonic pulse echo reflected on the other side may be received by the ultrasonic probe 12B. .

Further, in this reference example, since the ultrasonic pulse is incident obliquely on one side surface, it is possible to estimate the temperature distribution in the medium using the pitch catch method (oblique incidence method) and measure the temperature distribution. it can.

  As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various deformation | transformation implementation is possible within the range of the summary of this invention. For example, the medium is not limited to a solid but may be a gas or a liquid.

It is the whole apparatus explanatory drawing which shows Example 1 of this invention. It is a graph which shows the change of the amplitude and measurement temperature with respect to measurement time same as the above. It is a graph which shows the change of measurement temperature with respect to measurement time same as the above. It is a graph which shows the change of the temperature for every distance from a bottom face same as the above. BRIEF DESCRIPTION OF THE DRAWINGS It is whole explanatory drawing of the apparatus which shows the reference example 1 of this invention. It is a graph which shows the relationship between the temperature in a medium, and sound velocity same as the above. It is a graph which shows the change of the amplitude and measurement temperature with respect to measurement time same as the above. It is a graph which shows the change of the measurement temperature with respect to measurement time same as the above. It is sectional drawing of the principal part of the apparatus which shows the reference example 3 of this invention.

1 Measuring device 2 Plate material (medium)
3 Top (one side)
4 Bottom (contact surface)
6 Hot water (objects with different temperatures from the medium)
6A Molten aluminum (object with different temperature from medium)
Ts Contact surface temperature
T ₀ initial temperature
α Temperature conductivity
λ Thermal conductivity
ρ density
C Specific heat capacity
x Distance from contact surface
t Measurement time after contact (after heating)
u random variable
t _L Ultrasonic propagation time

Claims (5)

An ultrasonic probe is arranged on one side of the medium, the other side of the medium is heated, and the propagation time of the ultrasonic pulse propagating a certain distance in the medium and the known data of the medium are used in the medium. a temperature measuring method of the temperature distribution using ultrasound you measurements,
Using the propagation speed of the ultrasonic pulse with respect to the temperature of the medium and the temperature conductivity of the medium as the known data,
The ultrasonic pulse is incident from one side of the medium by the ultrasonic probe, and the propagation time of the ultrasonic pulse reflected from the other side of the medium is measured,
Assuming a function T (x, t) indicating the temperature distribution of the medium determined by the initial temperature of the medium, the temperature conductivity of the medium, and the measurement time after the heating,
The initial temperature obtained by measuring the surface temperature of the medium prior to the heating, the known temperature conductivity of the medium, the measurement time after the heating, and the propagation of the measured ultrasonic pulse. And the other side temperature and temperature of the medium using the formula of the propagation time of the ultrasonic pulse and the function T (x, t) determined from the propagation speed of the ultrasonic pulse with respect to the known temperature of the medium. A temperature measurement method using ultrasonic waves, characterized by calculating a distribution . The temperature measurement method using ultrasonic waves according to claim 1 , wherein the surface of the medium is one side surface, and the temperature of one side surface of the medium is measured to obtain the initial temperature . The propagation time formula is

In Equation 1, t _L is the propagation time of the ultrasonic pulse, V (T) is the sound velocity of the medium expressed as a function of temperature T, and this sound velocity V (T) is expressed by Equation 2 below. ,

In the above equation 2, A and B are constants specific to the medium,
The function T (x, t) is

In Equation 3, η is expressed by Equation 4 below,

In Equations 3 and 4, Ts is the other side surface temperature, T ₀ is the initial temperature of the medium, α is the temperature conductivity (α = λ / ρC: λ is the thermal conductivity of the medium, ρ is the density of the medium, and C is the medium density. 3. The temperature measurement method using ultrasonic waves according to claim 1 , wherein x is a distance from another side surface, t is a measurement time after heating, and u is a random variable . The temperature measurement method using ultrasonic waves according to any one of claims 1 to 3, wherein the ultrasonic pulse is incident obliquely from one side surface. The temperature measurement method using ultrasonic waves according to any one of claims 1 to 4 , wherein the frequency of the ultrasonic pulses is 100 kHz or more.

Images